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/* Spin locks for communication between threads and signal handlers.
Copyright (C) 2020-2022 Free Software Foundation, Inc.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
This file is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Bruno Haible <bruno@clisp.org>, 2020. */
#ifndef _ASYNCSAFE_SPIN_H
#define _ASYNCSAFE_SPIN_H
/* Usual spin locks are not allowed for communication between threads and signal
handlers, because the pthread_spin_* functions are not async-safe; see
<https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html>
section 2.4.3 Signal Actions.
This module provides spin locks with a similar API. It can be used like this,
both in regular multithreaded code and in signal handlers:
sigset_t saved_mask;
asyncsafe_spin_lock (&lock, &mask, &saved_mask);
do_something_contentious ();
asyncsafe_spin_unlock (&lock, &saved_mask);
The mask you specify here is the set of signals whose handlers might want to
take the same lock.
asyncsafe_spin_lock/unlock use pthread_sigmask, to ensure that while a thread
is executing such code, no signal handler will start such code for the same
lock *in the same thread* (because if this happened, the signal handler would
hang!). */
#include <signal.h>
#if defined _WIN32 && ! defined __CYGWIN__
# include "windows-spin.h"
typedef glwthread_spinlock_t asyncsafe_spinlock_t;
# define ASYNCSAFE_SPIN_INIT GLWTHREAD_SPIN_INIT
#else
typedef unsigned int asyncsafe_spinlock_t;
# define ASYNCSAFE_SPIN_INIT 0
#endif
#ifdef __cplusplus
extern "C" {
#endif
extern void asyncsafe_spin_init (asyncsafe_spinlock_t *lock);
extern void asyncsafe_spin_lock (asyncsafe_spinlock_t *lock,
const sigset_t *mask, sigset_t *saved_mask);
extern void asyncsafe_spin_unlock (asyncsafe_spinlock_t *lock,
const sigset_t *saved_mask);
extern void asyncsafe_spin_destroy (asyncsafe_spinlock_t *lock);
#ifdef __cplusplus
}
#endif
#endif /* _ASYNCSAFE_SPIN_H */
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